Microinjections of neurotensin into the periaqueductal gray matter (PAG) produced profound analgesia in the rat. This effect was accompanied by activation of neurons in the raphe magnus region and was attenuated by radio frequency lesions of this area. Opiates were found to increase the firing of zona compacta dopamine cells and decrease firing of zona reticulata cells following systemic administration. Micropressure ejection of opiates onto zona compacta cells had no effect while application to zona reticulata cells decreased their firing rate. Phencyclidine was found to activate the nigrostriatal dopamine pathways by an action in the substantia nigra. Type 1 opiate receptors were found to be localized on dopaminergic terminals in the striatum, while type 2 opiate receptors were found to be present on cell bodies intrinsic to this region. Neurotensin receptors were also found to be present on DA nerve terminals in the striatum, but not in the nucleus accumbens. Electrical stimulation of the substantia nigra elevated glucose utilization in the subthalamic nucleus, entopeduncular nucleus and globus pallidus.